1. Field of the Invention
The present invention relates to a multiplexer for use in a data processing system, and more particularly, to a multiplexer for connecting plural data processing units such as computers, word processors, to a printer.
2. Description of Related Art
Conventionally, in order to use a printer in common to plural data processing units such as host computers, word processors, there is provided a multiplexer between the printer and the data processing units. In a conventional multiplexer, there is provided an analogue switch for connecting a printer to one of plural data processing units, and the analogue switch is switched over by manual operation.
Recently, there has been manufactured an automatic scan type multiplexer capable of automatically switching over an analogue switch responsive to a control signal sent from a data processing unit.
On the other hand, a conventional printer performs only a printing operation responsive to data sent from the data processing unit. However, there have been proposed a printer capable of transmitting a response signal to the data processing unit responsive to a command sent therefrom, and also a printer capable of transmitting trouble information thereof to the data processing unit.
However, in the case that such a printer capable of transmitting and receiving data is used in common to plural data processing units, a conventional multiplexer only connects a specified data processing unit to the printer in both the transmission and reception operations. Namely, data outputted from the printer are outputted to only the specified data processing unit which outputs data to the printer.
For example, in the data to be outputted from the printer to the data processing units, there are data having a high emergency to be outputted to plural data processing units simultaneously, and data to be outputted to a data processing unit asynchronously with data received therefrom, namely, data to be outputted to a data processing unit other than a data processing unit from which data are received by the printer. The above-mentioned conventional multiplexer can not handle such data.